In a storage phosphor imaging system as described in U.S. Pat. No. Re. 31,847, reissued Mar. 12, 1985, to Luckey, a storage phosphor is exposed to an x-ray image of an object, such as the body part of a patient, to record a latent x-ray image in the storage phosphor. The latent x-ray image is read out by stimulating the storage phosphor with relatively long wavelength stimulating radiation such as red or infrared light produced by a helium neon gas laser or diode laser. Upon stimulation, the storage phosphor releases emitted radiation of an intermediate wavelength, such as blue light, in proportion to the quantity of x-rays that were received. To produce a signal useful in electronic image processing the storage phosphor is scanned in a raster pattern by a laser beam deflected by an oscillating or rotating scanning mirror or hologon. The emitted radiation from the storage phosphor is reflected by a mirror light collector and detected by a photodetector, such as a photomultiplier, to produce an electronic image signal. Typically the storage phosphor is translated in a page scan direction past the laser beam which is repeatedly deflected in a line scan direction perpendicular to the page scan motion of the storage phosphor to form a scanning raster pattern of a matrix of pixels.
In order to be able to reuse the storage phosphor, any residual image in the storage phosphor is erased by exposing it to light from suitable erase lamps, such as fluorescent lamps. If one or more erase lamps fail, erasure of the storage phosphor will be incomplete leaving a residual image in the storage phosphor. When it is reused, a new latent x-ray image will be recorded over the residual image resulting in unacceptable image degradation which can result in improper diagnosis. U.S. Pat. No. 4,754,145, issued Jun. 28, 1988, inventor Kobayashi, discloses a radiation image erase unit for use with stimulable phosphor sheets. The erase unit has a detecting means for detecting a reduction in the illuminance of an erasure light and for producing a signal indicative of the light reduction. The embodiment shown in FIG. 6 of this patent has a current sensor for each erasing light source to detect failure of individual light sources. This embodiment is expensive and complex.
There is thus a problem in the prior art of providing apparatus which detects the failure of lamps used in erasing a residual image in a storage phosphor and which is cost effective, efficient and relatively simple.